B.C. can learn from Asian tsunami

March 10, 2005, vol. 32, no. 5

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While B.C. can expect to endure a tsunami at some point in the future, according to SFU earth sciences professor John Clague, the loss of life would likely be two orders of magnitude less than the Dec. 26 earthquake/tsunami in Southeast Asia, where more than 150,000 were reported dead.

Clague, who holds a Tier I Canada Research Chair in natural hazard science, says Canada has a lot to learn from that earthquake/tsunami. There are a number of similarities between the Sumatran plate tectonics and the Cascadia subduction zone on B.C.'s west coast, which lies within the ring of fire.

This huge ring of volcanic and seismic activity stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands, and south along the coast of North and South America, contains over 75 per cent of the world's active and dormant volcanoes.

The two areas share similarities in seismic potential, Clague says, including long intervals, i.e. hundreds of years, between great earthquakes; long subduction zones; strong ground shaking when these earthquakes do occur; offshore fault areas; and similar plate tectonics.

"Canada has had some of the largest earthquakes on earth," says Clague. The last giant earthquake on the West Coast occurred on Jan. 26, 1700, triggering a large tsunami with waves several metres high as far away as Japan.

Scientists have established that date based on Japanese written records and geological evidence. Clague explains that scientists who study the sediments beneath tidal marshes on the coasts of Vancouver Island, Washington, and Oregon can see layers of tsunami sand sharply bounded by peat and mud. "The tsunamis occur repeatedly back through time, so it's inevitable that we'll experience something similar in the future."

A lesson of the southeast Asian tsunami is that we should re-examine our tsunami warning systems in the Pacific, notes Clague. Detecting and tracking a tsunami is relatively easy with high tech equipment. Getting the information to governments and then to the affected communities in time will be the problem. "We have a fairly good system," says Clague, "but we have to make sure that once the provincial government is notified of an impending tsunami, information reaches communities that will be affected and that the local officials take appropriate action.

Communities likely to be hit hard include Tofino and Port Alberni. Victoria also faces significant waves, but not Vancouver, which is protected by the Strait of Georgia.

Educating people in at-risk communities to recognize an approaching tsunami is another important issue, he says.

A giant earthquake at B.C.'s subduction zone would cause severe shaking along the west coast of Vancouver Island, followed 15-30 minutes later by a tsunami with waves ranging from several metres to perhaps 15 metres high.

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